INERTIAL DEPOSITION OF PARTICLES IN A BEND

Interest in the inertial deposition of particles in a bend has derived from a number of practical problems: for example , aerosol sampling, deposition of inhaled particles, and icing of aircraft air-intake ducts. The most important parameter which influences the impaction of particles in a bend is the Stokes number, P(=ρd Uo/18μa), where ρ is the density of the particle, d.the particle dia., Uo the average velocity of air, μ the viscosity of air, and α the radius of the tube. Experimental results with simple 90° bends with axial curvatures in the range 2.5-15 dia. and fluid Reynolds numbers from 100 to 1000 (Johnston and Muir, 1973) indicate that the impaction efficiency is 50 per cent at P 0.5 and that the axial curvature of the bends has no significant effects on the impaction efficiency. Theoretical calculations of the inertial deposition in 90°bends have been carried out by Landahl and Herrmann (1949) for parabolic velocity profile and by Hacker et al. (1953) for potential flow. These calculations were made either numerically or with an analog computer, because of the complexities of the equations governing the particle motion. This paper presents an analytical solution to the equation which describes the motion of a particle in an idealized flow in a 90°bend. In the idealized flow, the air velocity at any point in the tube is assumed to be a function of the distance from the axis of the bend alone. # B017503